Method for manufacturing optical laminates

Abstract

In an optical laminate in which a photopolymer layer containing a hologram is bonded to another layer, the color shift of the hologram before and after bonding is suppressed. [Solution] The optical laminate comprises a first layer which is a photopolymer layer containing a hologram, a second layer laminated on the first layer, and a molecular adhesive layer interposed between the first layer and the second layer.

Description

Technical Field

[0001] The present disclosure relates to an optical laminate.

Background Art

[0002] Patent Document 1 discloses an optical laminate including a photopolymer layer in which a hologram is recorded by exposure and an adhesive layer joined to the photopolymer layer, and further having another layer such as a base material adhered thereto. In the configuration of Patent Document 1, as the adhesive layer, a pressure-sensitive adhesive or a hot-melt adhesive such as a polyolefin-based adhesive or a urethane-based adhesive is used.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to Patent Document 1, it is described that the configuration of the disclosure can suppress color deviation of the hologram, that is, the color of the hologram in the laminate after adhesion changes from the color of the hologram in the state of the photopolymer layer alone before adhesion. However, in the configuration including the adhesive layer as described above, the suppressing effect on color deviation is not sufficient, and it may not be able to meet the high requirements for high color quality of holograms in recent years.

[0005] An object of the present disclosure is to suppress color deviation of a hologram before and after adhesion in an optical laminate in which a photopolymer layer including a hologram and another layer are adhered.

Means for Solving the Problems

[0006] One aspect of the present disclosure is an optical laminate having a first layer which is a photopolymer layer containing a hologram, a second layer laminated on the first layer, and a molecular adhesive layer interposed between the first layer and the second layer. [Effects of the Invention]

[0007] According to this disclosure, in an optical laminate in which a photopolymer layer containing a hologram is bonded to another layer, color shift of the hologram before and after bonding can be suppressed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing an optical laminate according to one embodiment of the present disclosure. [Figure 2] This is a schematic diagram showing an optical laminate according to the first embodiment. [Figure 3] This is a schematic diagram showing an optical laminate according to the second embodiment. [Figure 4] These are schematic diagrams of the layer configurations of typical examples and comparative examples. [Figure 5] This is the transmittance spectrum of the optical laminate of Example 1-1. [Figure 6] This is the transmittance spectrum of the optical laminate of Comparative Example 1. [Modes for carrying out the invention]

[0009] The specific embodiments of this disclosure will be described in more detail below with reference to the drawings. In this specification and the drawings, components having substantially the same functional configuration will be denoted by the same reference numerals to avoid redundant descriptions.

[0010] (optical laminate) Figure 1 shows an optical laminate 10 according to one embodiment of the present disclosure. The optical laminate 10 has a first layer 1 which is a photopolymer layer containing a hologram, a second layer 2 laminated on the first layer 1, and a molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2. In this specification, an optical laminate is a structure having optical functions, which is made up of multiple layers that are laminated together.

[0011] In this disclosure, the first layer 1 is a photopolymer layer containing a hologram, but the second layer 2 is not particularly limited. The second layer 2 may be, for example, a substrate for supporting or reinforcing the first layer 1, or it may be a photopolymer layer containing a hologram, similar to the first layer 1. The second layer 2 may also be a layer of material used in the optical field other than the substrate and the photopolymer layer, and may be a layer having predetermined optical properties, such as a predetermined refractive index or predetermined transmittance.

[0012] In this embodiment, the first layer 1 and the second layer 2 are bonded together via a molecular adhesive layer 3, thereby suppressing color changes (also called color shifts) of the hologram contained in the first layer 1. In this specification, suppression of hologram color changes refers to color changes that may occur due to bonding between layers, and more specifically, it means that the color changes of the hologram contained in the optical laminate are reduced or absent when comparing the state before bonding the first layer 1 and the second layer 2 with the state after bonding the first layer 1 and the second layer 2.

[0013] When the color change of the hologram due to adhesion between layers is large, it may not be possible to display the hologram in the desired color, and in particular, with multi-color holograms, it may not be possible to display an appropriate hologram image. In response to this, the inventors have found that by using a molecular adhesive layer 3 as the layer that adheres the first layer 1 and the second layer 2, the color change of the hologram can be effectively suppressed. As a result, high color quality of the hologram can be achieved. This is thought to be because the chemical and / or physical effect of the molecular adhesive layer 3 on the contact layer that comes into contact with the molecular adhesive layer 3 is small. Furthermore, since the thickness of the molecular adhesive layer 3 is thinner than that of conventional adhesive layers formed without molecular adhesives, it is thought that even if light penetrates the molecular adhesive layer 3, it has little effect on the optical properties of the optical laminate.

[0014] The color change of the hologram described above can be evaluated by measuring the transmittance spectrum of the hologram using a spectrophotometer or the like, and comparing the shape of the spectrum before and after bonding the first layer 1 and the second layer 2. For example, it can be evaluated by determining how much the wavelength of the peak of a predetermined peak in the transmittance spectrum shifts before and after bonding (the amount of change in wavelength), that is, by determining the difference between the wavelength (nm) at the peak of a predetermined peak in the spectrum before bonding and the wavelength (nm) at the peak of a predetermined peak in the spectrum after bonding. According to the optical laminate 10 of this disclosure, such a change in wavelength can be suppressed to 20 nm or less, 15 nm or less, 10 nm or less, or 5 nm or less.

[0015] In addition, since the color perceived by the hologram also changes depending on the transmittance, the color change of the hologram can also be evaluated by obtaining the amount of change in transmittance before and after adhesion. To obtain the change in transmittance, as described above, the transmittance spectrum of the hologram is measured using a spectrophotometer or the like, and the spectra are compared before and after adhering the first layer 1 and the second layer 2. Then, for example, the amount of change (the amount of change in transmittance) in the transmittance (%) at the peak of the maximum peak in the transmittance spectrum before and after adhesion is obtained, that is, the transmittance (%) at the peak of the maximum peak in the spectrum before adhesion and the transmittance (%) at the peak of the maximum peak in the spectrum after adhesion are obtained, and the difference (%pt) can be used for evaluation. According to the optical laminate 10 of the present disclosure, such an amount of change in transmittance can be suppressed to 30% or less, 20% or less, 10% or less, or 5% or less.

[0016] In addition, when suppressing the color change of the hologram as the top priority, it is also conceivable to directly stack the first layer 1 and the second layer 2 without interposing an adhesive layer between the first layer 1 and the second layer 2 to form a laminate. However, in that case, since the adhesion between layers is not sufficient, the strength is low, and a product that can withstand use as an optical laminate cannot be obtained. Therefore, the optical laminate according to the present embodiment is more specifically a product having sufficient interlayer adhesion that can function as an optical laminate while suppressing color change as described above.

[0017] Furthermore, the optical laminate 10 according to the present embodiment is also excellent in resistance under a predetermined environment, particularly high-temperature resistance. Here, high-temperature resistance means that even after high-temperature storage, the hologram has excellent color change and interlayer adhesion as described above. High-temperature resistance can be evaluated, for example, by evaluating the optical laminate 10 after storing it at a high temperature, specifically 60 °C or higher, preferably 80 °C or higher, for a predetermined time.

[0018] (Photopolymer layer) The first layer 1 is a layer in which a hologram is recorded on a photopolymer layer. The photopolymer layer used in this embodiment is not particularly limited as long as it is a layer composed of a photopolymer capable of recording a hologram. The photopolymer layer may contain, for example, a photopolymerizable monomer, a photoinitiator, and a binder. Also, the photo-oligomer layer may not contain a binder and may contain a matrix polymer, a writing monomer that is a photopolymerizable monomer, and a photoinitiator. In this case, the matrix polymer may be an amorphous thermoplastic resin. Examples of the matrix polymer include acrylic polymers, such as homopolymers or copolymers containing one or more monomers of (meth)acrylic acid, (meth)acrylic acid esters, and derivatives thereof, polybutyl acrylate, polyvinyl acetate, polyvinyl butyrate, gelatin, cellulose esters, cellulose ethers, silicone copolymers, polyurethanes, polybutadiene, polyisoprene, polyethylene oxide, epoxy resin polyamides, polycarbonates, and the like.

[0019] As the photopolymer layer, for example, a photopolymer film for hologram recording known in the art can be used. Commercially available products of the photopolymer film for hologram recording include the Bayfol® HX series manufactured by Covestro AG, such as Bayfol HX200. Note that commercially available products including the Bayfol series can be provided in a form in which the photopolymer layer is sandwiched between a cover film and a base film. In such a case, in the production of the optical laminate 10 according to this embodiment, in the lamination with the second layer 2, the cover film can be peeled off and bonded to the second layer 2. At that time, the production process may proceed with the base film left bonded to the photopolymer layer. Also, an optical laminate 10 including the base film may be configured.

[0020] The thickness of the photopolymer layer may be, for example, 1 μm or more, preferably 5 μm or more. Note that the thickness of the layers in the optical laminate 10 according to the present disclosure (including the thickness of the molecular adhesive layer 3) can be measured by an optical interference type film thickness meter or the like.

[0021] (Molecular adhesive layer) The molecular adhesive layer 3 is the layer that bonds the first layer 1 and the second layer 2 together. The molecular adhesive layer 3 is formed by interposing a molecular adhesive between the first layer 1 and the second layer 2 and allowing it to harden. In other words, the molecular adhesive layer 3 can be considered a cured product of the molecular adhesive. Here, the molecular adhesive refers to an adhesive containing a compound having two or more reactive functional groups. When the molecular adhesive is interposed between the first layer 1 and the second layer 2, the two or more reactive functional groups in the compound contained in the molecular adhesive chemically react with the functional groups on the respective surfaces of the adherends, the first layer 1 and the second layer 2, thereby forming a covalent bond between the first layer 1 and the second layer 2 via the compound.

[0022] The molecular adhesive used to form the molecular adhesive layer 3 is not particularly limited, but silane coupling agents, triazine-based molecular adhesives, etc., can be used.

[0023] Examples of silane coupling agents include amino-based silane coupling agents, epoxy-based silane coupling agents, vinyl-based silane coupling agents, acrylic-based silane coupling agents, methacrylic-based silane coupling agents, mercapto-based silane coupling agents, ureido-based silane coupling agents, isocyanate-based silane coupling agents, and combinations thereof. It is preferable to use an amino-based silane coupling agent and an epoxy-based silane coupling agent in combination.

[0024] Specific examples of amino silane coupling agents include N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyldimethoxysilane, N-2-(aminoethyl)-3-aminopropyldiethoxysilane, N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropyltriethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or their hydrochloride salts.

[0025] Commercially available amino silane coupling agents include KBM-602, KBM-603, KBM-903, KBE-603, and KBE-903 from Shin-Etsu Chemical Co., Ltd.; Z-6011, Z-6020, Z-6026, Z-6032, Z-6094, and Z-6610 from Toray Dow Corning Co., Ltd.; and A-1100, A-1110, A-1120, A-2120, and Y-9669 from Momentive Performance Materials Japan LLC.

[0026] Specific examples of epoxy silane coupling agents include 2-(3,4-epoxycyclohexyl)ethylmethyldimethoxysilane, 2-(3,4-epoxycyclohexyl)ethylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltrimethoxysilane, and 3-glycidoxypropyltriethoxysilane.

[0027] Commercially available epoxy silane coupling agents include KBM-303, KBM-402, KBM-403, KBE-402, and KBE-403 from Shin-Etsu Chemical Co., Ltd., SH6040, Z-6040, Z-6042, Z-6043, and Z-6044 from Toray Dow Corning Co., Ltd., and A-186, A-187, and A-1871 from Momentive Performance Materials Japan LLC.

[0028] The amino-based silane coupling agents and epoxy-based silane coupling agents described above can each be used individually or in combination of two or more. Furthermore, the molecular adhesive may contain silane coupling agents other than the amino-based and epoxy-based silane coupling agents, or it may contain molecular adhesives other than silane coupling agents, such as the triazine-based molecular adhesive described above.

[0029] Triazine-based molecular adhesives may be, for example, triazine ring-containing compounds having at least reactive group A and reactive group B (reactive group A is an amino group, azide group, diazomethyl group, diazirine group, mercapto group, isocyanate group, ureido group, or epoxy group; reactive group B is at least one functional group selected from the group consisting of a silanol group or a group that can generate a silanol group by hydrolysis). Specific examples of triazine-based molecular adhesives include 6-(3-triethoxysilylpropyl)amino-1,3,5-triazine-2,4-diazide and N,N'-bis(2-aminoethyl)-6-(3-trihydroxysilylpropyl)amino-1,3,5-triazine-2,4-diamine.

[0030] However, among the molecular adhesives mentioned above, it is preferable that the molecular adhesive is a silane coupling agent, and more preferably an amino-based silane coupling agent and an epoxy-based silane coupling agent, because it has a high effect in suppressing the color change of the hologram that may occur during bonding and improving the interlayer adhesion between the first layer 1 and the second layer 2, which are photopolymer layers.

[0031] When the molecular adhesive for forming the molecular adhesive layer 3 contains an amino-based silane coupling agent and an epoxy-based silane coupling agent, the ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent may be preferably 20:80 to 80:20 by mass ratio, more preferably 30:70 to 70:30, and even more preferably 60:40 to 40:60. By using the amino-based silane coupling agent and the epoxy-based silane coupling agent in the above ratio, a molecular adhesive layer 3 can be obtained that can improve the adhesion or bonding between layers. Therefore, an optical laminate can be obtained in which the color change of the hologram that may occur due to bonding between layers is suppressed and the adhesion between the first layer 1 and the second layer 2 is high. When manufacturing the optical laminate, it is preferable to use the molecular adhesive in the form of a solution (described later) of the silane coupling agent.

[0032] The thickness of the molecular adhesive layer 3 is thinner compared to the thickness of conventional adhesive layers formed using pressure-sensitive adhesives, hot-melt adhesives, etc. Therefore, the influence of the thickness of the adhesive layer interposed between the first layer 1 and the second layer 2 can be suppressed. In addition, because the molecular adhesive layer 3 is thin, the entire optical laminate 10 can be made thin, making it applicable to a variety of uses. The thickness of the molecular adhesive layer 3 can be less than 1 μm, 500 nm or less, 100 nm or less, or 50 nm or less.

[0033] The hologram contained in the first layer 1, which is a photopolymer layer, is preferably a volume hologram and may be either a reflective or a transmissive hologram. The hologram can be formed by exposing an interference pattern to a layer of hologram recording medium material, which is a precursor of the first layer 1, by, for example, irradiating it with ultraviolet light.

[0034] Since the optical laminate 10 according to this embodiment can be made thin and compact, it can be suitably used in small display devices. For example, it can be particularly suitably used in augmented reality (AR) devices, such as AR glasses like smart glasses, and head-mounted displays (HMDs).

[0035] Next, more specific embodiments of this disclosure will be described.

[0036] (First Embodiment) Figure 2 shows a schematic diagram of the optical laminate 10A according to the first embodiment. In the first embodiment, the second layer 2 is a substrate that supports the first layer 1, which is a photopolymer layer. That is, the laminate 10A according to the first embodiment comprises the first layer 1, which is a photopolymer layer containing a hologram; the second layer 2A, which is a substrate laminated on the first layer 1; and the molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2A.

[0037] Since the second layer is the base material 2A, it can reinforce the first layer 1 and prevent damage to the first layer 1, thereby improving the overall mechanical strength or mechanical robustness of the optical laminate 10A. The base material 2A is preferably a transparent base material. The base material 2A may also contain one or more of glass and resin, and is preferably composed of glass or resin. If the base material 2A is a resin, it may be a thermosetting resin or a thermoplastic resin, for example, poly(meth)acrylate resin, polycarbonate resin, polyurethane resin, epoxy resin, polyamide resin, polyimide resin, polyolefin resin, (meth)acrylic resin, cyclic polyolefin resin (norbornene-based resin), polyarylate resin, polystyrene resin, polyvinyl alcohol resin, cellulose resin such as triacetylcellulose resin film, polyester resin, polyethersulfone resin, or polysulfone resin.

[0038] The thickness of the base material 2A may be 1 μm or more, preferably 5 μm or more.

[0039] According to this embodiment, it is possible to suppress changes in the color of the hologram contained in the first layer 1 before and after bonding it to the substrate 2A.

[0040] (Second embodiment) Figure 3 shows the optical laminate 10B according to the second embodiment. In the optical laminate 10B, the first layer 1 is a photopolymer layer containing a hologram, and the second layer 2 is also a photopolymer layer containing a hologram. That is, the laminate 10B according to the second embodiment comprises the first layer 1, which is a photopolymer layer containing a hologram; the second layer 2B, which is a photopolymer layer containing a hologram, laminated on the first layer 1; and a molecular adhesive layer 3 interposed between the first layer 1 and the second layer 2B. In other words, the optical laminate 10B has a configuration in which two photopolymer layers having two holograms are laminated.

[0041] Here, the photopolymer layer used in the first layer 1 and the photopolymer layer used in the second layer 2B may be the same or different. That is, the composition and thickness of the photopolymer layer of the second layer 2B may be the same as or different from those of the photopolymer layer of the first layer 1. For example, the same commercially available hologram recording photopolymer film described above may be used for both the first layer 1 and the second layer 2B.

[0042] Furthermore, the optical laminate 10B shown in Figure 2 may have additional photopolymer layers containing holograms. Therefore, the number of photopolymer layers containing holograms included in the optical laminate 10B may be between 3 and 100. If the optical laminate 10B includes additional photopolymer layers containing holograms, these additional photopolymer layers can be bonded to the first layer 1 or the second layer 2 via an additional molecular adhesive layer.

[0043] In this configuration, where multiple photopolymer layers containing holograms are stacked, a color image can be displayed by guiding light of different wavelengths to each photopolymer layer separately for each color.

[0044] (Other embodiments) Furthermore, unlike the first and second embodiments, the second layer 2 (Figure 1) can be a different layer having a function other than the photopolymer layer containing the substrate and hologram. For example, the second layer 2 may be a layer having specific optical properties. These specific optical properties may be a specific refractive index, transmittance, reflectance, etc. It is preferable that the layer has a specific refractive index, and more preferably that it is a low refractive index layer.

[0045] When the second layer 2 is a low refractive index layer, one embodiment of the present disclosure is an optical laminate having a first layer which is a photopolymer layer containing a hologram, a second layer which is a low refractive index layer laminated on the first layer, and a molecular adhesive layer interposed between the first layer and the second layer. In this embodiment as well, the change in the color of the hologram before and after bonding between the layers is suppressed, allowing it to be displayed in an appropriate color, and the function of the low refractive index layer, i.e., its low refractive index, is not impaired. When the second layer 2 is a low refractive index layer, the refractive index of the second layer 2 is preferably 1.05 or more and 1.25 or less, more preferably 1.08 or more and 1.20 or less, and even more preferably 1.10 or more and 1.18 or less. As the material constituting the low refractive index layer, for example, the materials described in International Publication No. 2004 / 113966, Japanese Patent Publication No. 2013-254183, and Japanese Patent Publication No. 2012-189802 can be used. Specific examples of materials constituting the low refractive index layer include silicon compounds, organic polymers, polymerizable monomers, and curable resins. These may be used individually or in combination of two or more. Among these, it is preferable that the material constituting the low refractive index layer contains a silicon compound.

[0046] (Method of manufacturing optical laminates) The method for manufacturing the optical laminate 10 (including optical laminates 10A and 10B) described above may include, for example, preparing a first layer which is a photopolymer layer on which a hologram is recorded (S1), applying a molecular adhesive to one surface of the first layer (S2), laminating a second layer 2 onto the surface on which the molecular adhesive is applied (S3), and curing it (S4).

[0047] In step (S2) of applying the molecular adhesive to one surface of the first layer, the molecular adhesive can be used in solution form, preferably in aqueous solution form. By dissolving the molecular adhesive in a solvent to make a solution, a low-viscosity coating liquid can be obtained, so that the molecular adhesive layer 3 can be distributed as evenly as possible between the first layer 1 and the second layer 2 with as few gaps as possible. In addition, the thickness of the molecular adhesive layer 3 in the resulting optical laminate 10 can be made thinner. When using a molecular adhesive solution, the concentration of the molecular adhesive solution may be preferably 0.01% by mass or more and 30% by mass or less, more preferably 0.05% by mass or more and 20% by mass or less, and even more preferably 0.1% by mass or more and 10% by mass or less. For applying the molecular adhesive or the molecular adhesive solution, a reverse coater, gravure coater (direct, reverse or offset), bar reverse coater, roll coater, die coater, bar coater, rod coater, spin coater, spray coater, etc. can be used.

[0048] Furthermore, if the photopolymer layer is obtained in a form sandwiched between a cover film and a base film, in the step of applying the molecular adhesive (S2), the cover film is peeled off to expose one surface of the photopolymer layer, and the molecular adhesive is applied to that exposed surface.

[0049] Furthermore, at least one of the first and second layers may be subjected to a surface treatment, preferably a hydrophilization treatment or a wettability-enhancing treatment, on the surface that comes into contact with the molecular adhesive, before contact with the molecular adhesive. Such surface treatments may include corona treatment, plasma treatment, and the like.

[0050] The curing process (S4) may be performed immediately after the lamination process (S3), but pressure may be applied in the thickness direction (lamination direction) to the laminate, which is formed by laminating the first and second layers via a molecular adhesive. For example, a roller such as a hand roller can be used. By applying pressure, the molecular adhesive can be spread evenly between the layers without gaps, thereby improving interlayer adhesion.

[0051] The curing step (S4) is a step to promote the reaction between the molecular adhesive and the materials of the first layer 1 and the second layer 2 by means of heat, light, etc. For example, the curing step (S4) may be heating to a temperature of 60°C or higher and 120°C or lower.

[0052] The step of preparing the first layer, which is a photopolymer layer on which a hologram is recorded (S1), may include a hologram recording step (S1a) in which a hologram is recorded on the first layer, which is a photopolymer. In the hologram recording step (S1a), known means for recording a hologram on a photopolymer layer can be used. Hologram recording can be performed, for example, by irradiating the photopolymer layer with laser light of a predetermined wavelength using a known hologram recording laser device to form an interference pattern. If there are two or more photopolymer layers, for example, if both the first and second layers are photopolymer layers, a hologram is recorded on each layer. The hologram may be a volume hologram and may be a reflective hologram or a transmission hologram. The hologram may also be a monochromatic hologram or a multicolor hologram.

[0053] Furthermore, the hologram recording process (S1a) may not be included in the process of preparing the first layer (S1), and may be performed after the curing process (S4) or before the curing process (S4). [Examples]

[0054] The present disclosure will be described below based on examples.

[0055] <Materials used for sample preparation> • Holographic recording medium material (photosensitive material): Covestro AG's "Bayfol® HX200," a three-layer structure consisting of a polyethylene cover layer, a photopolymer layer, and a triacetylcellulose (TAC) layer. • Glass substrate: Corning Inc.'s "EAGLEXG (registered trademark)"

[0056] The following adhesives were prepared: Molecular adhesive A: An amino-based silane coupling agent (KBM-903, manufactured by Shin-Etsu Chemical Co., Ltd., 3-aminopropyltriethoxysilane, molecular weight 179.3) and an epoxy-based silane coupling agent (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a 50:50 mass ratio to prepare a molecular adhesive solution so that the total concentration of the silane coupling agent (also simply called the silane coupling agent concentration) reached a predetermined value. Molecular adhesive solutions with silane coupling agent concentrations of 0.1% by mass, 1% by mass, and 10% by mass were prepared separately.

[0057] Molecular adhesive B: An amino-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM-603", N-2-(aminoethyl)-3-aminopropyltriethoxysilane, molecular weight 222.4) and an epoxy-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM-403", 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a 50:50 mass ratio to prepare a molecular adhesive solution so that the total concentration of the silane coupling agent (also simply called the silane coupling agent concentration) reached a predetermined value. Molecular adhesive solutions with silane coupling agent concentrations of 0.1% by mass, 1% by mass, and 10% by mass were prepared separately.

[0058] Molecular adhesive C: An amino-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "X-12-972F") and an epoxy-based silane coupling agent (Shin-Etsu Chemical Co., Ltd. "KBM-403", 3-glycidoxypropyltrimethoxysilane, molecular weight 236.3) were added to distilled water in a 50:50 mass ratio to prepare a molecular adhesive solution so that the total concentration of the silane coupling agent (also simply called the silane coupling agent concentration) reached a predetermined value. Molecular adhesive solutions with silane coupling agent concentrations of 0.1% by mass, 1% by mass, and 10% by mass were prepared separately.

[0059] • Adhesive a: Nitto Denko Corporation, optical transparent adhesive sheet "LUCIACS CS986 UAS (thickness 25μm)"

[0060] <Fabrication of laminates> Using the materials described above, the following laminates were fabricated. Schematic diagrams of the laminates fabricated in Examples 1-1 and 2-1, as well as Comparative Examples 1 and 2, are shown in Figure 3.

[0061] (Example 1-1) A hologram (holographic diffraction grating) was recorded on the photopolymer layer of the holographic recording medium material from the triacetylcellulose (TAC) layer side using a semiconductor laser (Coherent, Verdi G series, peak wavelength 532 nm) by two-beam interference lithography. Subsequently, light from a xenon lamp light source was irradiated across the entire surface from the glass substrate side to cause fading. The polyethylene cover layer was peeled off from the material on which the hologram was recorded, exposing the photopolymer layer (first layer). Corona treatment was performed on the exposed surface of this photopolymer layer (treatment conditions: 1000 W·min / m²). 2 ) was applied. Separately, corona treatment (treatment conditions: 1000W·min / m²) was also applied to one side of the above glass substrate (second layer). 2 After the corona treatment was performed, a 10% by mass aqueous solution of molecular adhesive A was applied to the entire treated surface. Then, a photopolymer layer was laminated so that the corona-treated surface of the photopolymer layer was in contact with the aqueous solution of molecular adhesive A, thereby obtaining a laminate. Furthermore, pressure was applied to the entire laminate with a hand roller. This stretched the interposed molecular adhesive, ensuring that the molecular adhesive spread evenly between the photopolymer layer and the glass substrate. Subsequently, it was heated in a 90°C oven for 5 minutes to accelerate the reaction of the molecular adhesive. As a result, an optical laminate with a size of 50 mm × 50 mm was obtained, having a structure in which a photopolymer layer with a triacetylcellulose (TAC) layer and a glass substrate were bonded via the molecular adhesive layer.

[0062] (Examples 1-2) An optical laminate was obtained in the same manner as in Example 1-1, except that a 1.0% by mass aqueous solution of molecular adhesive B was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 1-1.

[0063] (Examples 1-3) An optical laminate was obtained in the same manner as in Example 1-1, except that a 0.1% by mass aqueous solution of molecular adhesive C was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 1-1.

[0064] (Example 2-1) A laminate was obtained in the same manner as in Example 1-1, using the above-mentioned hologram recording medium material as the second layer instead of the glass substrate. That is, a laminate was prepared in which two photopolymer layers were bonded together via a molecular adhesive. More specifically, a hologram was recorded on each of the two hologram recording medium materials and faded in the same manner as in Example 1-1. Then, the polyethylene cover layer was peeled off from each of the hologram-recorded media materials to expose the photopolymer layer, and the exposed surface of each photopolymer layer was subjected to corona treatment in the same manner as the corona treatment applied to the photopolymer layer in Example 1-1. A 10% by mass aqueous solution of molecular adhesive A was applied to the corona-treated surface of one of the photopolymer layers, and the other photopolymer layer was laminated so that the corona-treated surface of the photopolymer layer was in contact with it. Furthermore, after placing an adhesive (optical transparent adhesive (OCA) tape, thickness 25 μm) on the triacetylcellulose layer of one of the photopolymer layers, the corona-treated glass substrate used in Example 1-1 was laminated. Pressure was applied to the laminate obtained in this manner, and heating was performed under the same conditions as in Example 1-1. This resulted in an optical laminate having a structure in which two photopolymer layers, each measuring 50 mm x 50 mm and each containing a triacetylcellulose (TAC) layer, are bonded together via a molecular adhesive layer.

[0065] (Example 2-2) A laminate was prepared in the same manner as in Example 2-1, except that a 0.1% by mass aqueous solution of molecular adhesive B was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 2-1. A hologram was then recorded to obtain an optical laminate.

[0066] (Examples 2-3) A laminate was prepared in the same manner as in Example 2-1, except that a 10% by mass aqueous solution of molecular adhesive C was used instead of the 10% by mass aqueous solution of molecular adhesive A used in Example 2-1. A hologram was then recorded to obtain an optical laminate.

[0067] (Comparative Example 1) A laminate containing a hologram was obtained in the same manner as in Example 1-1, except that adhesive a was used instead of an aqueous solution of molecular adhesive A. More specifically, adhesive a (adhesive tape) was applied to the corona-treated surface of a glass substrate, and then a photopolymer layer was laminated so that the corona-treated exposed surface of the photopolymer layer was in contact with adhesive a, thereby obtaining an optical laminate.

[0068] (Comparative Example 2) A laminate was obtained in the same manner as in Example 1-1, except that the corona-treated surface of the photopolymer layer was directly brought into contact with the corona-treated surface of the glass substrate without using an adhesive or tack, thereby laminating the glass substrate and the photopolymer layer.

[0069] <Rating> The optical properties and interlayer adhesion of the obtained laminated samples were evaluated as follows.

[0070] (Optical properties) The optical properties were evaluated by determining (i) the change in diffraction wavelength before and after bonding, (ii) the change in transmittance before and after bonding, and (iii) (i) and (iv) (ii) after high-temperature storage.

[0071] (i) Change in diffraction wavelength For each example of laminate obtained as described above, i.e., laminates containing a photopolymer layer on which a hologram was recorded (post-adhesion samples), the transmittance spectrum was measured according to the method in accordance with JIS Z 8791:2011. More specifically, a spectrophotometer (Hitachi High-Tech Science UH4150) was used to obtain transmittance spectra in the range of 400 nm to 700 nm. The wavelength (nm) at the peak of the transmittance spectrum was recorded as the diffraction wavelength of the sample. On the other hand, in each example, a laminate (unadhesion samples) was also prepared in which the photopolymer layer and the second layer (glass substrate or photopolymer layer) were directly laminated without adhesive, and the hologram was recorded on the photopolymer layer. The transmittance spectrum of this laminate was measured in the same manner as above, and the diffraction wavelength was recorded in the same manner. The diffraction wavelength of the unadhesion sample was taken as λn (nm), and the diffraction wavelength of the post-adhesion sample was taken as λa (nm), and λa-λn (nm) was taken as the change in diffraction wavelength. Furthermore, the unbonded laminates in Examples 1-1 and 2-1 to 2-9, where the second layer was a glass substrate, were equivalent to the laminate prepared in Comparative Example 4.

[0072] (ii) Change in transmittance The transmittance (%) at the peak of the transmittance spectrum obtained as described above was recorded as the transmittance of the sample. The transmittance of the unadhered sample was Tn (%), and the diffraction wavelength of the adhered sample was Ta (%), with Ta-Tn (%pt) being the change in transmittance.

[0073] (iii) Change in diffraction wavelength after high-temperature storage The diffraction wavelength of the above bonded sample was determined using the same method as described in "(i) Change in diffraction wavelength" after storage at 80°C for 240 hours. The diffraction wavelength of the unbonded sample was λn, and the diffraction wavelength of the bonded sample after high-temperature storage was λa. H As, λa H -λn(nm) was defined as the change in diffraction wavelength after high-temperature storage.

[0074] (iv) Change in transmittance after high-temperature storage The transmittance of the bonded sample described above was determined by storing it in an environment at 80°C for 240 hours, using the same method as described in "(ii) Change in transmittance". The transmittance of the unbonded sample was Tn, and the diffraction wavelength of the bonded sample after high-temperature storage was Ta. H As Ta H -Tn(%pt) was defined as the change in transmittance after high-temperature storage.

[0075] (Interlayer adhesion) The interlayer adhesion of the hologram-containing laminates obtained in each example was evaluated by a grid test based on JIS K5400-8.5:1999. More specifically, 11 vertical and 11 horizontal cuts were made at 1 mm intervals on the triacetylcellulose (TAC) layer side of the obtained laminate using a utility knife, creating a total of 100 grids. Cellophane adhesive tape was applied over a length of approximately 50 mm to cover the surface where the cuts were made, and the tape was rubbed with an eraser to make it adhere. After leaving it for 1 to 2 minutes, the cellophane adhesive tape was lifted perpendicular to the surface by holding the end, and then instantly peeled off, and the number of grids that remained attached to the cellophane adhesive tape was counted. The number of grids that were not removed out of 100 was recorded. For example, if the number of grids that were not removed was 10, it was written as 10 / 100.

[0076] The results are shown in Table 1.

[0077] [Table 1]

[0078] Furthermore, Figure 4 shows the changes in the transmittance spectrum of the optical laminate of Example 1-1 before bonding, after bonding, and after high-temperature storage after bonding. Similarly, Figure 5 shows the changes in the transmittance spectrum of the optical laminate of Comparative Example 1 before bonding, after bonding, and after high-temperature storage after bonding.

[0079] Table 1 and Figure 4 show that in optical laminates where a photopolymer layer containing a hologram and a substrate are bonded via a molecular adhesive layer (Examples 1-1 to 1-3), and in optical laminates where photopolymer layers containing holograms are bonded to each other via a molecular adhesive (Examples 2-1 to 2-3), changes in wavelength and transmittance before and after bonding are suppressed, indicating that color shift is suppressed (good optical properties were obtained). Furthermore, these optical laminates were found to exhibit high interlayer adhesion.

[0080] On the other hand, the optical properties of optical laminates containing adhesive layers other than molecular adhesive layers (Comparative Examples 1-3) were lower than those of Examples 1-1 to 1-3. Furthermore, while the forms fabricated without adhesive showed optical properties equivalent to Examples 1-1 to 1-3, the interlayer adhesion was poor and they were not suitable for the normal use of optical laminates.

[0081] Furthermore, the aspects of this disclosure are, for example, as follows:

[0082] <1> An optical laminate comprising a first layer which is a photopolymer layer containing a hologram, a second layer laminated on the first layer, and a molecular adhesive layer interposed between the first layer and the second layer.

[0083] <2> The second layer is a substrate containing at least one of glass and resin. <1> The optical laminate described above.

[0084] <3> The second layer is a photopolymer layer containing a hologram. <1> The optical laminate described above.

[0085] <4> The molecular adhesive layer comprises a cured product of the molecular adhesive, and the molecular adhesive comprises a silane coupling agent. <1> from <3> An optical laminate as described in any of the following.

[0086] <5> The molecular adhesive comprises an amino-based silane coupling agent and an epoxy-based silane coupling agent. <4> The optical laminate described above.

[0087] <6> The ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent is 20:80 to 80:20 by mass. <5> The optical laminate described above.

[0088] <7> A method for manufacturing an optical laminate, comprising: preparing a first layer which is a photopolymer layer on which a hologram is recorded; applying a molecular adhesive to one surface of the first layer; laminating a second layer onto the surface on which the molecular adhesive is applied; and curing it.

[0089] <8> The molecular adhesive contains a silane coupling agent. <7> A method for manufacturing an optical laminate as described above.

[0090] <9> The molecular adhesive is applied in the form of a solution containing 0.01% to 30% by mass. <7> or <8> A method for manufacturing an optical laminate as described above. [Explanation of symbols]

[0091] 1. First layer (photopolymer layer) 2 Second layer 2A Second layer (base material) 2B Second layer (photopolymer layer) 3 molecular adhesive layer 10, 10A, 10B Optical Stacks

Claims

1. The first layer is a photopolymer layer containing a hologram, A second layer is stacked on the preceding first layer, An optical laminate having a molecular adhesive layer interposed between the above-mentioned first layer and the second layer.

2. The optical laminate according to claim 1, wherein the second layer is a substrate containing at least one of glass and resin.

3. The optical laminate according to claim 1, wherein the second layer is a photopolymer layer containing a hologram.

4. The optical laminate according to claim 1 or 2, wherein the molecular adhesive layer comprises a cured product of a molecular adhesive, and the molecular adhesive comprises a silane coupling agent.

5. The optical laminate according to claim 4, wherein the molecular adhesive comprises an amino-based silane coupling agent and an epoxy-based silane coupling agent.

6. The optical laminate according to claim 5, wherein the ratio of the amino-based silane coupling agent to the epoxy-based silane coupling agent is 20:80 to 80:20 by mass ratio.

Images